Understanding Negative Current in Discharging Capacitors

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SUMMARY

The discussion centers on the concept of negative current in discharging capacitors, specifically addressing the equations governing current flow and potential differences. It establishes that as time progresses, the potential difference across the capacitor and resistor decreases, leading to a reduction in current, defined as I = dq/dt. The term "negative current" is clarified to mean either a negative rate of charge flow or current flowing in the opposite direction, with the consensus being that negative dq/dt indicates a decrease in current over time, not a reversal in direction.

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  • Understanding of Ohm's Law
  • Familiarity with capacitor discharge equations
  • Knowledge of current flow and charge (dq/dt)
  • Basic principles of electrical circuits
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Homework Statement


upload_2017-9-1_11-24-38.png


Homework Equations

The Attempt at a Solution


A)Clearly,
##V_A - V_B >0
\\V_C - V_D >0## as the current flows from higher potential to the lower potential.
As the time passes on, the potential difference across the capacitor as well as the resistor goes on decreasing. Consequently, according to Ohm's law, the current goes on decreasing. This means that either the speed of the charged particles is decreasing or the no. of charged particles passing through the resistor is decreasing.
Assuming that it is the no. of charged particles which is decreasing, keeping the speed constant,
the current defined ,here , as I = ## \frac {dq}{dt} ## is negative.

So, the concept "negative current" has two meanings : 1) ## \frac {dq}{dt} ## is negative.
2) the current is flowing in the opposite direction. Right?

Now,
##[V_A - V_B= q/C ] = [ V_C - V_D = - \frac {dq}{dt} R##
Is this correct so far?
 

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Pushoam said:
Is this correct so far?
Yes.
 
Pushoam said:
) dqdtdqdt \frac {dq}{dt} is negative.
This is correct.
Pushoam said:
the current is flowing in the opposite direction. Right?
No. In this case, the direction shown in the diagram is correct. So negative dq/dt means current reduces over time.
 

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